Support different function key modes

From http://aperiodic.net/phil/archives/Geekery/term-function-keys.html

mentioned in issue #5701 (closed)

Keep in mind that this doc is 10+ years old.

I've never seen a keyboard with a physical F13 or higher key; although there are Shift, Ctrl etc. modifiers that can be pressed. Apparently they're meant to be encoded as off by 12 (Shift), 24 (Ctrl) and 36 (Shift+Ctrl) when talking about F13..F48 which I find an utterly stupid legacy notation.

Not sure what those two xterms were, today's xterm matches neither (the second xterm column is right with F1..F4, but not with modifier+F1..F4, these were changed a few years ago).

MGT is long dead.

Just FYI: https://bugzilla.gnome.org/show_bug.cgi?id=600659 comments 74-79-ish.

Thanks for the heads up. This bug is really meant to remind me to make function key handling less of an awful hack than it is today and to let a million standards bloom. Also, Apple makes this thing:

I guess f13-f19 are there for good looks more than anything.